U.S. Pat. No. 3,842,194 to Clemens discloses a high density information, e.g., video, disc for use in a playback system utilizing variable capacitance. In one configuration of the Clemen's system information representative of recorded pictures and sound is encoded in the form of a relief pattern in a relatively fine spiral groove in the surface of the disc record. For example, groove widths of about 2.6 micrometers and groove depths of about 0.5 micrometer may be used. During playback a pickup stylus about 2.0 micrometers wide having a thin conductive electrode thereon, for example about 0.2 micrometer thick, engages the groove as the record is rotated by a supportive turntable. Capacitive variations between the stylus electrode and the record surface are sensed to recover the prerecorded information.
Clemens discloses in the aforementioned patent a triangular shaped stylus having one face coated with a conductive coating. In particular, transition metals such as hafnium, titanium or tantalum may be used as the conductive metal coating.
Keizer, in U.S. Pat. No. 4,162,510, incorporated herein by reference, discloses a playback stylus which may be used with ths grooved capacitive disc system. The keel tipped pickup stylus comprises a dielectric support element having a body, a constricted terminal portion and shoulders interconnecting the body with the constrictive terminal portion. The constrictive terminal portion is defined by a prow, a substantially flat rear surface remote from said prow, side surfaces extending from the edges of the rear surface, a bottom surface extending from the bottom edge of the rear surface and a plurality of additional surfaces extending from the prow and intersecting the bottom and the side surfaces. A conductive layer on the substantially flat rear surface serves as the electrode. The maximum separation between the substantially parallel side surfaces is less than the given groove width. The bottom surface of the stylus may be shaped to conform to the shape of the groove.
However, a problem has been encountered with the use of a metal conductive coating as the electrode. When the stylus contacts the record surface the portion of metal coating closest to the record surface may wear away. Furthermore, problems have been encountered at the interface between the metal coating and the diamond dielectric support material. Poor adhesion is often observed with concomitant flaking off of the metal coating.
The copending application of C. W. Mueller et al entitled "Ion Implanted Diamond Video Disc Stylus", Ser. No. 134,906, which is incorporated herein by reference, describes a diamond video disc stylus in which a conductive layer is formed at the diamond surface by ion implantation. The ion implantation process leads to increased conductivity of the diamond, sufficient at minimum ion dosage levels to be useful in the above-described playback system.